We revisit the H i size–mass (
$D_{\rm H\,{\small I}}$
–M
H i
) relation of galaxies with a sample of more than 500 nearby galaxies covering over five orders of magnitude in H i mass and more than 10 ...B-band magnitudes. The relation is remarkably tight with a scatter σ ∼ 0.06 dex, or 14 per cent. The scatter does not change as a function of galaxy luminosity, H i richness or morphological type. The relation is linked to the fact that dwarf and spiral galaxies have a homogeneous radial profile of H i surface density in the outer regions when the radius is normalized by D
H i
. The early-type disc galaxies typically have shallower H i radial profiles, indicating a different gas accretion history. We argue that the process of atomic-to-molecular gas conversion or star formation cannot explain the tightness of the D
H i
–M
H i
relation. This simple relation puts strong constraints on simulation models for galaxy formation.
ABSTRACT
We present the discovery of another odd radio circle (ORC) with the Australian Square Kilometre Array Pathfinder (ASKAP) at 944 MHz. The observed radio ring, ORC J0102–2450, has a diameter ...of ∼70 arcsec or 300 kpc, if associated with the central elliptical galaxy DES J010224.33–245039.5 (z ∼ 0.27). Considering the overall radio morphology (circular ring and core) and lack of ring emission at non-radio wavelengths, we investigate if ORC J0102–2450 could be the relic lobe of a giant radio galaxy seen end on or the result of a giant blast wave. We also explore possible interaction scenarios, for example, with the companion galaxy, DES J010226.15–245104.9, located in or projected on to the south-eastern part of the ring. We encourage the search for further ORCs in radio surveys to study their properties and origin.
Predictions for ASKAP neutral hydrogen surveys Duffy, Alan R.; Meyer, Martin J.; Staveley‐Smith, Lister ...
Monthly notices of the Royal Astronomical Society,
11 November 2012, Letnik:
426, Številka:
4
Journal Article
Recenzirano
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ABSTRACT
The Australian Square Kilometre Array Pathfinder (ASKAP) will revolutionize our knowledge of gas‐rich galaxies in the Universe. Here we present predictions for two proposed extragalactic ...ASKAP neutral hydrogen (H i) emission‐line surveys, based on semi‐analytic models applied to cosmological N‐body simulations. The ASKAP H i All‐Sky Survey, known as Widefield ASKAP L‐band Legacy All‐sky Blind surveY (WALLABY), is a shallow 3 π survey (z = 0–0.26) which will probe the mass and dynamics of over 6 × 105 galaxies. A much deeper small‐area H i survey, called Deep Investigation of Neutral Gas Origins (DINGO), aims to trace the evolution of H i from z = 0 to 0.43, a cosmological volume of 4 × 107 Mpc3, detecting potentially 105 galaxies. The high‐sensitivity 30 antenna ASKAP core (diameter ∼2 km) will provide an angular resolution of 30 arcsec (at z = 0). Our simulations show that the majority of galaxies detected in WALLABY (87.5 per cent) will be resolved. About 5000 galaxies will be well resolved, i.e. more than five beams (2.5 arcmin) across the major axis, enabling kinematic studies of their gaseous discs. This number would rise to 1.6 × 105 galaxies if all 36 ASKAP antennas could be used; the additional six antennas provide baselines up to 6 km, resulting in an angular resolution of 10 arcsec. For DINGO this increased resolution is highly desirable to minimize source confusion, reducing confusion rates from a maximum of 10 per cent of sources at the survey edge to 3 per cent. We estimate that the sources detected by WALLABY and DINGO will span four orders of magnitude in total halo mass (from 1011 to 1015 M⊙) and nearly seven orders of magnitude in stellar mass (from 105 to 1012 M⊙), allowing us to investigate the process of galaxy formation across the last four billion years.
Abstract
We investigate shock structures driven by merger events in high-resolution simulations that result in a galaxy with a virial mass
M
≈ 10
12
M
⊙
. We find that the sizes and morphologies of ...the internal shocks resemble remarkably well those of the newly detected class of odd radio circles (ORCs). This would highlight a so-far overlooked mechanism to form radio rings, shells, and even more complex structures around elliptical galaxies. Mach numbers of
= 2–3 for such internal shocks are in agreement with the spectral indices of the observed ORCs. We estimate that ∼5% of galaxies could undergo merger events, which occasionally lead to such prominent structures within the galactic halo during their lifetime, explaining the low number of observed ORCs. At the time when the shock structures are matching the physical sizes of the observed ORCs, the central galaxies are typically classified as early-type galaxies, with no ongoing star formation, in agreement with observational findings. Although the energy released by such mergers could potentially power the observed radio luminosity already in Milky Way–like halos, our predicted luminosity from a simple, direct shock acceleration model is much smaller than the observed one. Considering the estimated number of candidates from our cosmological simulations and the higher observed energies, we suggest that the proposed scenario is more likely for halo masses around 10
13
M
⊙
in agreement with the observed stellar masses of the galaxies at the center of ORCs. Such shocks might be detectable with next-generation X-ray instruments like the Line Emission Mapper (LEM).
We introduce SoFiA, a flexible software application for the detection and parametrization of sources in 3D spectral line data sets. SoFiA combines for the first time in a single piece of software a ...set of new source-finding and parametrization algorithms developed on the way to future H i surveys with ASKAP (WALLABY, DINGO) and APERTIF. It is designed to enable the general use of these new algorithms by the community on a broad range of data sets. The key advantages of SoFiA are the ability to: search for line emission on multiple scales to detect 3D sources in a complete and reliable way, taking into account noise level variations and the presence of artefacts in a data cube; estimate the reliability of individual detections; look for signal in arbitrarily large data cubes using a catalogue of 3D coordinates as a prior; provide a wide range of source parameters and output products which facilitate further analysis by the user. We highlight the modularity of SoFiA, which makes it a flexible package allowing users to select and apply only the algorithms useful for their data and science questions. This modularity makes it also possible to easily expand SoFiA in order to include additional methods as they become available. The full SoFiA distribution, including a dedicated graphical user interface, is publicly available for download.
Missing Mass in Collisional Debris from Galaxies Bournaud, Frédéric; Duc, Pierre-Alain; Brinks, Elias ...
Science (American Association for the Advancement of Science),
05/2007, Letnik:
316, Številka:
5828
Journal Article
Recenzirano
Odprti dostop
Recycled dwarf galaxies can form in the collisional debris of massive galaxies. Theoretical models predict that, contrary to classical galaxies, these recycled galaxies should be free of nonbaryonic ...dark matter. By analyzing the observed gas kinematics of such recycled galaxies with the help of a numerical model, we demonstrate that they do contain a massive dark component amounting to about twice the visible matter. Staying within the standard cosmological framework, this result most likely indicates the presence of large amounts of unseen, presumably cold, molecular gas. This additional mass should be present in the disks of their progenitor spiral galaxies, accounting for a substantial part of the so-called missing baryons.
A Search for the Host Galaxy of FRB 171020 Mahony, Elizabeth K.; Ekers, Ron D.; Macquart, Jean-Pierre ...
Astrophysical journal. Letters,
11/2018, Letnik:
867, Številka:
1
Journal Article
Recenzirano
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We report on a search for the host galaxy of FRB 171020, the fast radio burst (FRB) with the smallest recorded dispersion measure (DM; DM = 114 pc cm−3) of our ongoing ASKAP survey. The low DM ...confines the burst location within a sufficiently small volume to rigorously constrain the identity of the host galaxy. We identify 16 candidate galaxies in the search volume and single out ESO 601-G036, an Sc galaxy at redshift z = 0.00867, as the most likely host galaxy. Ultraviolet and optical imaging and spectroscopy reveal that this galaxy has a star formation rate of approximately 0.1 M yr−1 and oxygen abundance 12 + log(O/H) = 8.3 0.2, properties that are remarkably consistent with the galaxy hosting the repeating FRB 121102. However, in contrast to FRB 121102, follow-up radio observations of ESO 601-G036 show no compact radio emission above a 5 limit of L2.1GHz = 3.6 × 1019 W Hz−1. Using radio continuum observations of the field, combined with archival optical imaging data, we find no analog to the persistent radio source associated with FRB 121102 within the localization region of FRB 171020 out to z = 0.06. These results suggest that FRBs are not necessarily associated with a luminous and compact radio continuum source.
2MTF – VI. Measuring the velocity power spectrum Howlett, Cullan; Staveley-Smith, Lister; Elahi, Pascal J ...
Monthly notices of the Royal Astronomical Society,
11/2017, Letnik:
471, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Abstract
We present measurements of the velocity power spectrum and constraints on the growth rate of structure fσ8, at redshift zero, using the peculiar motions of 2062 galaxies in the completed ...2MASS Tully–Fisher survey (2MTF). To accomplish this we introduce a model for fitting the velocity power spectrum including the effects of non-linear redshift space distortions (RSD), allowing us to recover unbiased fits down to scales k = 0.2 h Mpc−1 without the need to smooth or grid the data. Our fitting methods are validated using a set of simulated 2MTF surveys. Using these simulations we also identify that the Gaussian distributed estimator for peculiar velocities of Watkins & Feldman is suitable for measuring the velocity power spectrum, but sub-optimal for the 2MTF data compared to using magnitude fluctuations δm, and that, whilst our fits are robust to a change in fiducial cosmology, future peculiar velocity surveys with more constraining power may have to marginalize over this. We obtain scale-dependent constraints on the growth rate of structure in two bins, finding
$f\sigma _{8} = 0.55^{+0.16}_{-0.13},0.40^{+0.16}_{-0.17}$
in the ranges k = 0.007–0.055, 0.55–0.150 h Mpc−1. We also find consistent results using four bins. Assuming scale-independence we find a value
$f\sigma _{8} = 0.51^{+0.09}_{-0.08}$
, a ∼16 per cent measurement of the growth rate. Performing a consistency check of general relativity (GR) and combining our results with cosmic microwave background data only we find
$\gamma = 0.45^{+0.10}_{-0.11}$
, a remarkable constraint considering the small number of galaxies. All of our results are completely independent of the effects of galaxy bias, and fully consistent with the predictions of GR (scale-independent fσ8 and γ ≈ 0.55).
ABSTRACT
Odd radio circles (ORCs) are recently-discovered faint diffuse circles of radio emission, of unknown cause, surrounding galaxies at moderate redshift (z ∼ 0.2 – 0.6). Here, we present ...detailed new MeerKAT radio images at 1284 MHz of the first ORC, originally discovered with the Australian Square Kilometre Array Pathfinder, with higher resolution (6 arcsec) and sensitivity (∼ 2.4 μJy/beam). In addition to the new images, which reveal a complex internal structure consisting of multiple arcs, we also present polarization and spectral index maps. Based on these new data, we consider potential mechanisms that may generate the ORCs.
ABSTRACT
Many disc galaxies in clusters have been found with bulges of similar age or younger than their surrounding discs, at odds with field galaxies of similar morphology and their expected ...inside-out formation. We use the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations to test potential origins for this difference in field and cluster galaxies. We find, in agreement with observations, that on average disc-dominated field galaxies in the simulations have older inner regions, while similar galaxies in groups and clusters have similarly aged or younger inner regions. This environmental difference is a result of outside-in quenching of the cluster galaxies. Prior to group/cluster infall, galaxies of a given present-day mass and morphology exhibit a similar evolution in their specific star formation rate (sSFR) profiles. Post-infall, the outer sSFRs of group and cluster galaxies significantly decrease due to interstellar medium stripping, while the central sSFR remains similar to field galaxies. Field disc galaxies instead generally retain radially increasing sSFR profiles. Thus, field galaxies continue to develop negative age gradients (younger discs), while cluster galaxies instead develop positive age gradients (younger bulges).
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